Children who have lysosomal disease experience declines in health status and central nervous system integrity which result in motor, communication, self-care, learning and behavioral challenges. Medical interventions such as enzyme replacement therapy (ERT) and hematopoietic stem cell transplantation can improve the health and functioning of children with lysosomal disease. To date, however, there is no established system for evaluating the health status, developmental status, behavioral outcomes or functional outcomes of these preschool-aged children across time and differing settings. The primary objective of this study is to develop a valid and reliable telephone-based data-gathering system for obtaining health status data, developmental status data, behavioral outcomes data, and functional outcomes data which reflect skills of daily living including feeding, moving, communicating and responding to others.